Apterichtus mysi, Hibino, Yusuke, 2015

Hibino, Yusuke, 2015, A review of the finless snake eels of the genus Apterichtus (Anguilliformes: Ophichthidae), with the description of five new species, Zootaxa 3941 (1), pp. 49-78 : 70-73

Apterichtus mysi n. sp.

Figures 13–14 , Tables 1 , 5

Holotype. BPBM 11843, 298 mm, male, Marquesas Islands, Fatu Hiva Island, off point at N end of Hanauu Bay (10o29’26”S, 138o38’56”W), depth 35 m, captured using rotenone over sand bottom by J.E. Randall, D. Cannoy and R. McNair, 21 Apr. 1971.

Paratypes. 9 specimens, 167–301 mm. BPBM 41104, 277 mm, gravid female, and CAS 234136, 298 mm, collected with the holotype. BPBM 11908, 249 mm, Marquesas Islands, Tahuata Island, off point at S end of Vaitahu Bay (09o57'S, 139o05'W), depth 35–40 m, captured using rotenone over sand and rubble bottom by J.E. Randall et al., 23 Apr. 1971. BPBM 11891, 241 mm, Marquesas Islands, Nuku Hiva Island, Baie Hatuarua, off Nuka River (10o29'S, 138o38'W), depth 53–59 m, captured using dredge by D.M. Devaney, 18 Sept. 1967. MNHN 2001-1089, 5 (167–301 mm), Nuku Hiva, depth 45–64 m, 24 Aug. 1997.

Non-paratypes. MNHN 2014-2819, two specimens, 160+ and 240+ mm (extrapolated total lengths ~ 190 mm and 280 mm), badly damaged during capture but identifiable as this new species.

Diagnosis. An elongate species with: tail 2.2–2.4, head 17–18, and body depth 58–69 in total length; snout moderately pointed in lateral view, dorsal profile ca. 45–50o above lower jaw; 3 preopercular pores and 3 pores in supratemporal canal; teeth conical, uniserial on jaws and vomer; 5–6 vomerine teeth; body mostly pale in preservative, with fine brown speckling on the dorsal surface of body and tail; and MVF 75–148, total vertebrae 146–153 (n=10).

Counts and measurements (in mm) of the holotype (those of the paratypes summarized in Table 5 ). Total length 298; head 17.3; trunk 147.7; tail 133; body depth at gill openings 4.9; body width at gill openings 4.0; body depth at anus 4.0; body width at anus 3.6; head depth at branchial basket 5.7; head width at branchial basket 4.7; snout 3.4; tip of snout to rictus 3.2; tip of snout to tip of lower jaw 2.5; eye diameter 1.3; interorbital distance 1.6; gill-opening length ~1.8; isthmus width ~1.0. Vertebral formula 76–151. Lateral-line pores difficult to discern, 6 in branchial region, ~80 pores before the anus.

Description. Body elongate, nearly cylindrical throughout, snout and tail tip sharply pointed, depth at gill openings 59–83 in TL. Branchial basket slightly wider and deeper than body. Head and trunk 1.8 in TL; head 17–18 in TL, 7.8–9.2 in trunk. Snout pointed, its underside somewhat rounded and bisected by a groove ( Figs. 13–14 ). Lower jaw included, its tip slightly in advance of eye. Slope of dorsal surface of snout approximately 35° relative to underside of snout. Lower jaw included, its tip slightly in advance of eye; snout extends beyond tip of lower jaw by slightly less than lower jaw length; upper and lower lips meet when mouth is closed. Mouth moderately elongate. Rictus well behind rear margin of eye. An obvious crease extends posteriorly in upper lip from beneath eye to rictus. Eye moderately developed, 4.2–5.1 in upper jaw and 12–15 in head, its anterior margin behind tip of lower jaw, its center in advance of middle of upper jaw. Anterior nostril within a short tube, approximately one-fourth the diameter of the eye, its base in anterior third of snout and anterolaterally directed when viewed from above. Posterior nostril opens in outer lip beneath anterior margin of eye. Branchial openings low, ventral; branchial region modestly expanded, creating a bulbous region in posterior half of head.

Head pores ( Fig. 13 ) small. Single median interorbital and temporal pores. Supraorbital pores 1+4, infraorbital pores 5-6+2, supratemporal pores 3, lower jaw pores 4, preopercular pores 3. Lateral-line pores difficult to discern, 6 above branchial region, ~80 before anus.

Teeth ( Fig. 14 ) uniserial, small, conical and slightly recurved. Intermaxillary with a chevron of 5–6 teeth (the largest in the jaw), followed by a short gap and a linear row of 5 small vomerine teeth. Jaw teeth nearly subequal, small, 11–12 teeth in each side of upper jaw and 11–12 teeth in each side of lower jaw.

Body mostly colorless in alcohol preservative (preserved in formalin and transferred to alcohol more than 15 years ago), however a fine brown speckling is present on the body and tail of some specimens.

Size. The largest specimen examined is 301 mm, a female with eggs ~ 0.6–0.9 mm in diameter.

Etymology. Named in honor of Mysi Hoang of the California Academy of Sciences for her many contributions to ichthyology, to be treated as a noun in apposition.

Distribution. Known from the Marquesas Islands, Polynesia, captured over sand with associated rock and coral reef bottoms using ichthyocides and dredges between 35–64 m depth.

Remarks. The new species differs from its congeners in the size and shape of its snout, the position of its eye, its cephalic pore configuration, and in its vertebral numbers. It is most similar to those species which share its cephalic pore condition of possessing 3 supratemporal pores and 3 preopercular pores, viz. Apterichtus anguiformis , A. australis , A. equatorialis , A. flavicaudus and A. kendalli . It differs considerably from the New World species A. equatorialis and A. kendalli in having a shorter tail (2.2–2.4 vs. 1.8–2.0 in TL) and in having slightly more total vertebrae (146–153 vs. 137–145).

Apterichtus mysi is most similar in cephalic appearance and vertebral number to A. australis and A. flavicaudus but differs from them in having a shorter and less acute snout (17–20% vs. 19–23% of HL), a shorter anterior nostril tube (approximately 4 times in eye vs. 3 times in eye) and the tip of its lower jaw is in advance of a line beneath the anterior margin of the orbit (vs. lower jaw tip beneath the anterior margin of the orbit). It differs from its other congeners in having fewer supratemporal and preopercular pores. The subtle differences between A. mysi and those congeners appear to fit a pattern that other Marquesan eels display. David G. Smith of the National Museum of Natural History advised McCosker (2010:36) “that widely-dispersed species of Indo-Pacific eels occasionally possess endemic forms in the Marquesas”, a pattern that has become more substantiated by subsequent collections and studies.

A 197 mm specimen of A. klazingai was collected together with the new species at Nuku Hiva (MNHN 2001- 1089).

Figures

FIGURE 13. Head of holotype of Apterichtus mysi, BPBM 11843, 298 mm. Drawn by J. McCosker.

FIGURE 14. Dentition of holotype of Apterichtus mysi, BPBM 11843, 298 mm. Drawn by J. McCosker.

Tables

TABLE 5. Counts and proportions (in thousandths) of the holotype and 7 paratypes of Apterichthus mysi n. sp. TL = total length. HL = head length. Vertebral counts are based on all 10 types.

	holotype	mean	range
TL (mm)	294	---	241–301
HL/TL	58	57	55–58
Head and trunk/TL	554	554	546–565
Tail/TL	446	446	425–454
Upper jaw/HL	358	346	327–366
Snout/HL	197	181	172–197
Eye/HL	75	75	66–81
Interorbital/HL	93	93	83–104
Gill opening/HL	104	112	96–128
Isthmus/HL	58	52	39–61
Depth at gill opening/TL	16	15	12–17
Width/depth at gill opening	816	845	790–935
Preanal vertebrae	76	74.9	72–78
Total vertebrae	151	147.9	146–153